The goal of the BMT CTN is to conduct phase II and III multicenter trials to advance the hematopoietic stem cell transplantation (HSCT) technology and measure therapeutic advantages over non transplant therapies for hematopoietic disorders. The scientific environment of the Moffitt BMT Program will contribute to the success of the BMT CTN by providing fertile ground for the development of original concepts for multicenter trials, enrolling patients, and contributing to disseminate new knowledge in the field of HSCT. Specific Aim 1 (proposed concept): Test the efficacy of ATG for GVHD prophylaxis before unrelated donor HSCT in a phase III multicenter trial implemented by the BMT CTN. The addition of ATG to standard pharmacologic prophylaxis will provide more effective prevention of grade lll-IV acute GVHD following unrelated donor HSCT. ATG will also reduce chronic GVHD and improve patient quality of life. The efficacy of ATG for acute GVHD prophylaxis will not be fully realized until effective approaches are developed to reduce the incidence of Epstein-Barr Virus (EBV) reactivation and prevent post-transplant lymphoproliferative disorders (PTLD), that are the most serious complications of ATG therapy. In ATG- treated patients, we will test the hypothesis that rituximab prophylaxis can reduce the incidence of EBV reactivation compared to rituximab preemptive therapy. Specific Aim 2: Collaborate with the BMT CTN in the design and conduct of multicenter studies and the dissemination of the results. Although novel ideas start from individuals or teams of investigators commonly at a single center, significant advances in medical care occur through multicenter phase III randomized trials. The Moffitt Cancer Center has a fully established clinical and translational research program in HSCT with infrastructure to facilitate 400 HSCT per year. Our team brings expertise in GVHD immunobiology, myeloma therapy, behavioral therapy in cancer patients and evidence-based research. We perform now more than 350 HSCT including 130 allogeneic HSCT per year and pledge to make available BMT CTN trials available to patients receiving autologous and allogeneic HSCT in our institution. RELEVANCE (See instructions): The Blood and Marrow Transplantation Clinical Trial Network will advance transplantation technology by improving efficacy and decreasing toxicity of hematopoietic stem cell transplantation. The number of patients cured from blood disorders will increase. The Moffitt Cancer Center will contribute to the conception of multicenter clinical trials, patient enrollment, data analysis and knowledge dissemination.